Yes, yes, I know there's a list of creative writing tips… about, anyway, but that's not open-edit and it's just sort of a guide to How Not to Look Like an Idiot. And I know this is common tread ground, but that doesn't make it any less useful.

So! What I'm asking here is to create an easily referable respitory of various tropes, formats, ideas and whatnot which can successfully be used to create horror, fear, creepiness, mild perturbance, disamusedness, whatever you might call it, that people have noticed over time. I know how I sound, but good threads have been started in the past by fools, so…

Overview

““Nothing is so frightening as what’s behind a closed door, [William F. Nolan] said. You approach the door in the old, deserted house, and you hear something scratching at it. The audience holds its breath along with the protagonist as she/he approaches the door. The protagonist throws it open, and there is a ten-foot-tall bug. The audience screams, but this particular scream has an oddly relieved sound to it. “A bug ten feet tall is pretty horrible,” the audience thinks, “but I can deal with a ten-foot-tall bug. I was afraid it might be a hundred feet tall.” …What’s behind the door or lurking at the top of the stairs is never as frightening as the door or staircase itself. And because of this, comes the paradox: artistic work of horror is almost always a disappointment. It is the classic no-win scenario. You can scare people with the unknown for a long, long time, but sooner or later, as in poker, you have to turn your cards up. You have to show the audience what’s behind it…
“There is and always has been a school of horror writers (I am not among them) who believe that the way to beat this rap is to never open the door at all. …The exciting thing about radio at its best was that it bypassed the question of whether to open the door or leave it closed. Radio, by the very nature of the medium, was exempt. For the listeners during the years 1930 to 1950 or so, there were no visual expectations to fulfill in their set of reality.”
- Stephen King, Danse Macabre, emphasis added

Audio, as King expresses, is a well suited medium for the genre of horror. The audience, deprived of the visual, is able to imagine the objects of their terror. Audio is different from video in having different conventions in its mode of storytelling, however, which can be disconcerting to audiences accustomed to the false dichotomy of text-based and visual storytelling.

Four Types of Scares

“Terror on top, horror below it, and lowest of all, the gag reflex of revulsion. My own philosophy as a writer of horror fiction is to recognize these distinctions because they are sometimes useful, but to avoid any preference for one over the other on the grounds that one effect is somehow better than another. The problem with definitions is that they have a way of turning into critical tools—and this sort of criticism, which I would call criticism-by-rote, seems to me needlessly restricting and even dangerous. I recognize terror as the finest emotion… and so I will try to terrorize the reader. But if I cannot terrify him/her, I will try to horrify; and if I cannot horrify, I’ll go for the gross-out. I’m not proud.”
-Stephen King, Danse Macabre

In his non-fiction book Danse Macabre (a fine work I highly recommend for any aspiring horror writer), Stephen King divides scares into three types: terror, horror, and revulsion. I will humbly add a fourth - shock/surprise - which does not neatly fit in any of his three categories but is present in horror fiction nonetheless.

Terror

“The finest emotion is terror, that emotion which is called up in the tale of The Hook and also in that hoary old classic, “The Monkey’s Paw.” We actually see nothing outright nasty in either story; in one we have the hook and in the other there is the paw, which, dried and mummified, can surely be no worse than those plastic dogturds on sale at any novelty shop. It’s what the mind sees that makes these stories quintessential tales of terror. It is the unpleasant speculation called to mind when the knocking on the door begins in the latter story and the grief-stricken old woman rushes to answer it. Nothing is there but the wind when she finally throws the door open… but what, the mind wonders, might have been there if her husband had been a little slower on the draw with that third wish?”
- Stephen King, Danse Macabre

In audio format, terror is caused by absence more than presence. The absence of sound, or the absence of explanation. We know the monster is out there, but all we hear are crickets in the night. When is it going to appear? Alternatively, we hear the banging at the door. We don’t know what beastie is trying to get in, but it cannot be good.

Terror also applies to the moment of dawning comprehension where the audience realizes that their preconception was wrong and the situation is worse than they originally feared. The banging on the door is not coming from a monster trying to get inside – the monster is already inside. That scene in Aliens where the characters are briefly confused how the monsters could be inside the room, as their motion detectors say. The moment of “oh, crap!” when they realize the aliens are above them in the air ducts – that is terror.

Audio also provides an opportunity for terror many media lack: the ability to abruptly remove stimuli. If one is listening to a scene where the characters are walking through the woods at night, the background ambience would likely include crickets and/or frogs, the occasional owl, and similar. If that suddenly disappears, either by fading out or by an abrupt cut (as would occur if one hit the “pause” button), that itself can inspire terror in the audience.

Horror

“…Horror, that emotion of fear that underlies terror, an emotion which is slightly less fine, because it is not entirely of the mind. Horror also invites a physical reaction by showing us something which is physically wrong… As we have already pointed out, the old man in “The Monkey’s Paw” is able to wish the dreadful apparition away before his frenzied wife can get the door open. In Tales from the Crypt, the Thing from Beyond the Grave is still there when the door is open wide, big as life and twice as ugly.”
- Stephen King, Danse Macabre

In audio format, if terror is caused by absence, horror is caused by presence. We hear the monsters – the shrieks, the screams, the snarls – and we “see” them as well (perhaps more aptly, the characters see them, and we hear the characters’ descriptions and reactions).

This can be quite difficult to pull off well. A zombie might be scary, but the sound of a low moan “Ooouuuuunnnnnggghhhrrrrrrr” is unlikely to scare an adult. Since the rise of television in the 1950s, we have become accustomed to being scared by horrific sights rather than horrific sounds. Therefore, creativity is needed. Stargate SG-1 does a good job of creating horror-inspiring sounds with its replicators. The eeeTICK eeeTICK eeeTICK sound of each mechanical spider’s legs is scary enough; multiply it thousands of times and it becomes nightmare inspiring.

Revulsion

“There is a third level—that of revulsion. This seems to be where the “chest-burster” from Alien fits… the gross-out.”
- Stephen King, Danse Macabre

Again, we as a society have become accustomed to disgusting sights more than disgusting sounds. In some ways, this is a boon to audio. Drips, squelches, and other disgusting sounds can be as effective or more than gallons of fake blood in a visual medium. And, unlike the visual, the source of the sound need be nothing like that for which it stands in. A sound effects guru acquaintance of mine once needed to create the sound of a man’s skin being turned inside out. He put on some rubber gloves and recorded the sound of peeling them off, inside out. When played back without the visual stimulus of the gloves being removed, it was disturbingly believable.

Shock/Surprise

This is when something scares the audience by startling them.

In an audio format, sudden sounds fall here. Jump scare chords, unexpected sound effects, and the like all fall into this category. Use these judiciously; overuse rapidly becomes irritating and drives away audiences.

Agreed, but the referenced scene in Alien I would attribute more as Shock/Surprise followed by Horror (that thing was living inside him…that face thing put it there). The scene from Alien that would be Revulsion based is in the special edition where Dallas is seen cocooned (I am very surprised that Skerrit allowed live maggots to be dumped all over him).

I'll note that Mr.King's comment about radio is also applicable to the peculiar format of the SCP article. Due to the fact the text is for the most part dry and technical, you're forcing the reader to bring in their own emotional reaction. Losing the typical narrative cues we're used to in prose is akin to losing the visual cues in a radio broadcast. Because part of the story is missing, the audience is forced to come up with it themselves.

Thank you for this! Horror is a new genre for me to write in (I'm well-acquainted with elaborate nightmares, I've had trouble figuring out what exactly freaks me out about them and how to reproduce that feeling), so it's nice to see it deconstructed a bit.

in all the horror I have written (Nothing on this site yet) I have always let the audience wonder about what it was. Often times I would ask what they thought the monster was, and they would all give me a different answer, usually something spawned off their own worst fears. It was extremely interesting to hear, and made writing it so much more exciting.

I think that a good horror story should fill you with a sense of unease — at least prior to the climax — rather than try to shock you. Here's an example of uneasiness done well: the famous sleepwalking scene from Macbeth, as played by Judi Dench. http://youtu.be/IOkyZWQ2bmQ

The first time I saw this scene, I found it very awkward to watch, particularly the wail at 4:10. At the time, I just assumed it was a hammy performance and giggled nervously. In retrospect, however, I think it's an excellent example of horror — she wails in such a surreal way, for such an unnaturally long time, that she forces the audience to become really uncomfortable, regardless of how they feel about her acting.

Also, this goes for any piece of writing, but it's particularly good for avoiding narm in horror: when you've finished a draft, put it away somewhere and don't look at it for a week. You'll find it a lot easier to spot errors when you come back to it.